Stock TPI Throttle-bodies have dual 48mm openings and are able to be ported out to 52mm and replacing valves. 58mm TBs are new units.
Flow and HP ratings for Throttle-bodies:
                               Flow (cfm)           Approx. Max NA HP
Stock                           668                           300
Stock w/airfoil          710                           350
52mm w/airfoil         835                           400
54mm (AS&M)       900                           450
58mm                       1050                           500
Click on any image below for an enlargement (~500K) image.
Stock TB, measured front diameter "flaired out" (51mm)
Stock TB, measured rear diameter lip (49mm)
Stock TB, measured rear diameter chamber (48mm)
Edelbrock TB (pn 3804), measured front diameter "flared out" (58mm)
Edelbrock TB, measured front diameter "flared out" (58mm)
Edelbrock TB, measured rear diameter (58mm)
Edelbrock TB, fullview with stock TPS and top cover plate installed
Edelbrock TB, fullview with stock IAC housing installed
Edelbrock TB, View thru into ported plenum
Edelbrock TB, View thru into ported plenum
Am I being picky, or should the product look like the picture on the box?
First product I received, closeup
Second product I received, compared to box picture
Second product I received, closeup